Why Do Chrome and Firefox Render Percentage Heights Differently on Block-Level Elements?

Heights Rendering Differently in Chrome and Firefox

Question:

When setting a block-level element's height to a percentage (e.g., 1%) without explicitly setting the height of its parent, why do Chrome and Firefox compute the height differently, with Chrome considering the child's bottom margin and Firefox not?

Answer:

The CSS standards state that if the containing block's height is not specified explicitly, a percentage height computes to "auto."

However, different browsers have implemented this provision differently:

• Webkit browsers (Chrome, Safari) adhere to the traditional interpretation, requiring the parent to have a set height for percentage heights to work on in-flow children.
• Firefox and IE have broadened their interpretation to accept flex heights as well.

This deviation from the spec has led to rendering inconsistencies, with some browsers using flex heights and others requiring a set parent height.

Alternative Solutions:

To ensure consistent rendering in all browsers, consider using one of the following alternatives:

• Set the parent's display to "flex" to automatically enable full height for children using align-items: stretch.
• Use position: absolute and position: relative on the parent and child elements, respectively, with the child having height: 100%; width: 100%. This allows percentage heights to work on child elements even without a specified parent height.

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